Vascular smooth muscle remodeling plays a key role in the development of several pulmonary diseases, including pulmonary hypertension, a fatal disease that culminates in heart failure. Thus, there is a need for research in this area. The objective of this proposal is to study the molecular basis of the remodeling process in vivo by generating and characterizing a novel genetic mouse model. Such models are necessary to define the particular role of key gene products and ensuing signaling pathways in disease pathogenesis. The Rho GTPase and its primary effect or, Rho kinase (ROCK), mediate many vascular smooth muscle cell responses such as contractility and growth which are also implicated in the remodeling process. Data in cultured cells have shown that Rho/ROCK participate in pulmonary vascular smooth muscle cell proliferation and acto-myosin cytoskeletal changes. Moreover, ROCK is implicated in the development of experimentally-induced pulmonary hypertension in rodents. However, much of the in vivo data is based on the use of pharmacological ROCK inhibitors (Y27632, fasudil) that are not specific; therefore the in vivo role of ROCK in vascular smooth muscle remodeling remains to be independently determined. There are two ROCK genes, and our hypothesis is that ROCK1plays a distinct role in vascular smooth muscle remodeling and in pulmonary hypertension development, but this has not been studied in a genetic animal model. On this basis, Specific Aim 1 will generate a unique vascular smooth muscle-targeted ROCK1 gene knock-out (KO) mouse strain. Specific Aim 2 will characterize the phenotype of the targeted KO strain. Aim2 will include in vivo studies at baseline and in response to stress such as hypoxia, and studies of cellular and signaling responses of cultured vascular smooth muscle cells derived from the ROCK1KO strain. Overall, the Aims will generate and characterize a novel genetic ROCK animal model, and test the hypothesis in vivo that ROCK1 contributes to remodeling and pulmonary hypertensive disease.